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https://issues.apache.org/jira/browse/MESOS-7122?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15871413#comment-15871413
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Yan Xu commented on MESOS-7122:
-------------------------------
True. For the motivating example we can try to remove blocking, i.e.,
{{Future::await()}} when calling the HDFS wrapper.
I think this ticket looks at this from another angle, though.
{{Future::await}} is still called in many places in the code base and if all
active actors block like this, we *may* deadlock. However we only deadlock when
"all these actors are blocked on futures that require an additional thread from
the worker thread pool to unblock". i.e., if these futures can be unblocked by
threads outside the pool like zookeeper or {{io::poll}} then we won't deadlock.
The point of this JIRA is that subprocess reaping may be suitable to be made
like the zookeeper client or {{io::poll}} and it's used widely enough but its
purpose special enough that it may warrant a special actor (or non-actor) for
this.
So to me, yes the libprocess users can be more careful when writing code to
minimize blocking but libprocess as a library can also help reduce the chances
of deadlock for some common cases.
> Process reaper should have a dedicated thread to avoid deadlock.
> ----------------------------------------------------------------
>
> Key: MESOS-7122
> URL: https://issues.apache.org/jira/browse/MESOS-7122
> Project: Mesos
> Issue Type: Bug
> Components: libprocess
> Reporter: James Peach
>
> In a test environment, we saw that libprocess can deadlock when the process
> reaper is unable to run.
> This happens in the Mesos HDFS client, which synchronously runs a {{hadoop}}
> subprocess. If this happens too many times, the {{ReaperProcess}} is never
> scheduled to reap the subprocess statuses. Since the HDFS {{Future}} never
> completes, we deadlock with all the threads in the call stack below. If there
> was a dedicated thread for the {{ReaperProcess}} to run on, or some other way
> to endure that is is scheduled we could avoid the deadlock.
> {noformat}
> #0 0x00007f67b6ffc68c in pthread_cond_wait@@GLIBC_2.3.2 () from
> /lib64/libpthread.so.0
> #1 0x00007f67b6da12fc in
> std::condition_variable::wait(std::unique_lock<std::mutex>&) () from
> /usr/lib64/libstdc++.so.6
> #2 0x00007f67b8b864f6 in process::ProcessManager::wait(process::UPID const&)
> () from /usr/lib64/libmesos-1.2.0.so
> #3 0x00007f67b8b8d347 in process::wait(process::UPID const&, Duration
> const&) () from /usr/lib64/libmesos-1.2.0.so
> #4 0x00007f67b8b51a85 in process::Latch::await(Duration const&) () from
> /usr/lib64/libmesos-1.2.0.so
> #5 0x00007f67b834fc9f in process::Future<Bytes>::await(Duration const&)
> const () from /usr/lib64/libmesos-1.2.0.so
> #6 0x00007f67b833d700 in
> mesos::internal::slave::fetchSize(std::basic_string<char,
> std::char_traits<char>, std::allocator<char> > const&,
> Option<std::basic_string<char, std::char_traits<char>, std::allocator<char> >
> > const&) () from /usr/lib64/libmesos-1.2.0.so
> #7 0x00007f67b833df5e in
> std::result_of<mesos::internal::slave::FetcherProcess::fetch(mesos::ContainerID
> const&, mesos::CommandInfo const&, std::basic_string<char,
> std::char_traits<char>, std::allocator<char> > const&,
> Option<std::basic_string<char, std::char_traits<char>, std::allocator<char> >
> > const&, mesos::SlaveID const&, mesos::internal::slave::Flags
> const&)::{lambda()#2} ()()>::type
> process::AsyncExecutorProcess::execute<mesos::internal::slave::FetcherProcess::fetch(mesos::ContainerID
> const&, mesos::CommandInfo const&, std::basic_string<char,
> std::char_traits<char>, std::allocator<char> > const&,
> Option<std::basic_string<char, std::char_traits<char>, std::allocator<char> >
> > const&, mesos::SlaveID const&, mesos::internal::slave::Flags
> const&)::{lambda()#2}>(std::result_of const&,
> boost::disable_if<std::result_of
> const&::is_void<std::result_of<mesos::internal::slave::FetcherProcess::fetch(mesos::ContainerID
> const&, mesos::CommandInfo const&, std::basic_string<char,
> std::char_traits<char>, std::allocator<char> > const&,
> Option<std::basic_string<char, std::char_traits<char>, std::allocator<char> >
> > const&, mesos::SlaveID const&, mesos::internal::slave::Flags
> const&)::{lambda()#2} ()()> >, void>::type*) () from
> /usr/lib64/libmesos-1.2.0.so
> #8 0x00007f67b833a3d5 in std::_Function_handler<void
> ()(process::ProcessBase*), process::Future<Try<Bytes, Error> >
> process::dispatch<Try<Bytes, Error>, process::AsyncExecutorProcess,
> mesos::internal::slave::FetcherProcess::fetch(mesos::ContainerID const&,
> mesos::CommandInfo const&, std::basic_string<char, std::char_traits<char>,
> std::allocator<char> > const&, Option<std::basic_string<char,
> std::char_traits<char>, std::allocator<char> > > const&, mesos::SlaveID
> const&, mesos::internal::slave::Flags const&)::{lambda()#2} const&, void*,
> {lambda()#2},
> mesos::internal::slave::FetcherProcess::fetch(mesos::ContainerID const&,
> mesos::CommandInfo const&, std::basic_string<char, std::char_traits<char>,
> std::allocator<char> > const&, Option<std::basic_string<char,
> std::char_traits<char>, std::allocator<char> > > const&, mesos::SlaveID
> const&, mesos::internal::slave::Flags const&)::{lambda()#2}
> const&>(process::PID<process::AsyncExecutorProcess> const&, process::Future
> (process::PID::*)(mesos::internal::slave::FetcherProcess::fetch(mesos::ContainerID
> const&, mesos::CommandInfo const&, std::basic_string<char,
> std::char_traits<char>, std::allocator<char> > const&,
> Option<std::basic_string<char, std::char_traits<char>, std::allocator<char> >
> > const&, mesos::SlaveID const&, mesos::internal::slave::Flags
> const&)::{lambda()#2} const&, void*), {lambda()#2},
> mesos::internal::slave::FetcherProcess::fetch(mesos::ContainerID const&,
> mesos::CommandInfo const&, std::basic_string<char, std::char_traits<char>,
> std::allocator<char> > const&, Option<std::basic_string<char,
> std::char_traits<char>, std::allocator<char> > > const&, mesos::SlaveID
> const&, mesos::internal::slave::Flags const&)::{lambda()#2}
> const&)::{lambda(process::ProcessBase*)#1}>::_M_invoke(std::_Any_data const&,
> process::ProcessBase*) () from /usr/lib64/libmesos-1.2.0.so
> #9 0x00007f67b8b85ede in
> process::ProcessManager::resume(process::ProcessBase*) () from
> /usr/lib64/libmesos-1.2.0.so
> #10 0x00007f67b8b8fc8f in
> std::thread::_Impl<std::_Bind_simple<process::ProcessManager::init_threads()::{unnamed
> type#1} ()()> >::_M_run() () from /usr/lib64/libmesos-1.2.0.so
> #11 0x00007f67b6da1470 in ?? () from /usr/lib64/libstdc++.so.6
> #12 0x00007f67b6ff8aa1 in start_thread () from /lib64/libpthread.so.0
> #13 0x00007f67b6a3faad in clone () from /lib64/libc.so.6
> {noformat}
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